In several communications systems, the data to be transmitted is compressed so that the available bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172, incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818, incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, incorporated herein by reference.
A program transport stream is formed by multiplexing individual elementary streams which share a common time base (i.e., the same 27 MHz clock source). The elementary streams comprise encoded video, audio or other bit streams. The elementary streams may be, but do not have to be, in a packetized elementary stream (PES) format prior to transport multiplexing. A PES consists of a packet header followed by a packet payload. As the elementary streams are multiplexed, they are formed into transport packets and a control bit stream that describes the program (also formed into transport packets) is added.
There are many instances where there is a need to switch from one encoded or compressed bitstream to another. When switching from one compressed MPEG video bitstream to another, appropriate measures must be taken in the transmission order of the picture bitstream to assure proper subsequent presentation of the decoded pictures, without time gaps. Such time gaps result in undesirable video or audio artifacts (e.g., blank screen due to buffer overflow/underflow, poor "lip sync" and the like). Heretofore there has not existed a seamless splicing method and apparatus for splicing transport streams to one another.
Therefore, a need exists in the art for a method and apparatus for splicing compressed digital information bitstreams.